Chemical Reaction, an Extremely Fast Process at Molecular Level

1 CHEMICAL REACTION, AN EXTREMELY FAST PROCESS AT MOLECULAR LEVEL 

Why is fast chemical synthesis needed The most appropriate answer to this question is because we can just do it with our present knowledge and technologies. Extremely fast reactions that are complete within a second used to be difficult to control on a preparative scale because we were using conventional macrobatch reactors. However, we are now able to conduct such reactions in a controlled manner with the aid of microflow systems constructed with micro-structured reactors and microreactor technology. 

As we have already discussed in Chapter 2, chemical reactions are essentially extremely fast processes at the molecular level. It takes several hundred femtoseconds for the conversion of a single starting molecule to a single product molecule through a transition state. Bimolecular reactions also take similar reaction times at the molecular level. Therefore, if all reactant molecules in a reactor react at once or coherently, the reaction time should be several hundred femtoseconds. This is the scientific limit of reaction times. If we can conduct the reaction in this way on a preparative scale, the synthesis finishes within several hundred femtoseconds. From a technical point of view, we are presently far from that point. Reaction times for chemical synthesis usually range 

Flash Chemistry Fast Organic Synthesis in Microsystems Jun-ichi Yoshida 

However, another reason why flash chemistry is needed is that our way of synthesizing compounds is currently changing. For example, combinatorial synthesis of chemical libraries has become very popular in academia and industry and on-site, on-demand synthesis is expected to be popular in the future. These new trends in chemical synthesis increase the demand for flash chemistry. 

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